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Oct. 7, 1958 A.' v. CHAMPAGNAT ETAL SEPARATION OF HYDROCARBONS BY MEANS OF UREA Filed May 20. 1955 2 Sheets-Sheet 2 a INVENTORS:

ALFRED v. CHAMPAGNAT CHyLES L. ERNE 0 I M I I 43 i.

ATTORNEYS the rate of formation of the solid derivatives.

United States Patent SEPARATION OF HYDROCARBONS BY MEANS OF UREA Alfred Valentin Champagnat and Charles Louis Vernet,

Paris, France, assignors to The British Petroleum Company Limited Application May 20, 1953, Serial No. 356,184

Claims priority, application France May 24, 1952 9 Claims. (Cl. 260-965) This invention relates to a process for the separation of hydrocarbons. More particularly, the invention relates to a process for the extractive crystallization of mineral oil fractions, by means of urea.

It is well known that urea forms crystalline solid adducts with straight chain and slightly branched chain hydrocarbons but does not form solid compounds with naphthenes, highly branched compounds or aromatics. By the use of urea a method has been developed for refining petroleum fractions by resolution of the fractions into chemical types by forming the above solid compounds, removing the remaining liquid phase (known as the urea adduction raffinate), decomposing the solid compounds and recovering from the product the liberated hydrocarbons (known as the urea adduction extract).

It is also known that when mixtures of normal parafiins and normal olefins are subjected to urea adduction that by reason of the different reactivity of these types of compounds toward urea, a degree of separation may be elfected, the parafiins tending to pass into the extract and the olefins of similar boiling range tending to pass into the rafiinate. Similarly a degree of separation may be effected between normal mono-olefins and normal di-olefins, by urea adduction, since the former compounds tend to pass into the extract and the latter compounds tend to pass into the rafiinate.

Furthermore, it is known that the presence of methanol or other low molecular weight alcohols, in admixture with urea and fractions undergoing treatment, accelerates It has also been stated in the prior art that mixtures of methanol and water may be employed as the activating agent.

According to some proposals the urea is employed in solution in a solvent or solvent mixture which, in general, is not miscible with hydrocarbons. Usually, operating in this manner, the solution of urea must be saturated at the temperature of the reaction with hydrocarbons and there must be a certain quantity of urea present in addition to that necessary for saturation (at the temperature of the reaction), this excess urea constituting the available urea for reaction with the normal and slightly branched chain paraffins to produce the solid complex. Under these conditions, the reaction between the mixture of hydrocarbons of the petroleum fraction to be treated and the urea, partially in solution, gives rise to the formation of a dense emulsion, generally of the oil in water type, and consisting of a continuous liquid phase, comprising the saturated solution of urea, and a discontinuous liquid phase, formed of hydrocarbons that have not reacted with the urea. The emulsion carries in suspension, two solid phases, that is, solid complex crystals and surplus urea crystals which have not formed a complex.

The complex obtained usually takes the form of a mass of interlaced crystalline needles, of very large apparent volume. Thus the separation of rafiinate from the thick, thixotropic complex containing emulsion has been found very diflicult.

2,855,390 Patented Oct. 7, 1958 ICC In certain processes filtration is used, which leaves on the filter a mass of complex crystals and surplus urea crystals. However, this mass of crystals retains a large proportion of raffinate, which has to be eliminated by washing with the aid of a solvent, if it is desired to obtain a good output and good selectivity in separation. These filtration and washing operations usually call for laborious and costly apparatus.

Other processes have recourse to decantation for separating the raflinate from the aforementioned complex containing emulsion. Nevertheless, this emulsion is for the most part very stable and thus, although it is often possible to separate, by simple decantation, a major proportion of the rafiinate, the remainder thereof is retained in the phase comprising urea solution (which contains also the surplus complex and urea crystals) thereby adversely aifecting the selectivity of the process.

Methods for the separation of the ralfinate from the emulsion have been described in the specifications filed in respect of our copending United States patent application Serial No. 278,627, filed March 26, 1952, now U. S. Patent No. 2,719,106, and Serial No. 286,829, filed May 8, 1952, now U. S. Patent No. 2,710,855. In United States patent application Serial No. 278,627 there is described the use of a ternary solvent which is non-miscible with the hydrocarbons, comprising in its preferred form water, methanol and ethylene glycol. In United States patent application Serial No. 286,829, there is described the operation of a process using urea containing 0.5 to 5% (preferably 1%) of biuret. The use of this ternary solvent and of urea containing biuret permits the formation of crystals of urea and complex of very small dimensions, so that the droplets of rafiinate in suspension in the emulsion join and are decanted more readily. Also according to United States patent application Serial No. 278,627, when using the ternary solvents described therein, the decantation of the raflinate is completed by the addition to the emulsion of a small quantity of aqueous methanol derived by distilling part of the urea solution.

It is an object of the present invention to provide an improved process for the extraction crystallization of hydrocarbon mixtures by the use of urea. More particularly, it is an object of the invention to provide a process of this type in which the rafiinate is separated in convenient manner from the emulsified product formed by reaction of the hydrocarbon mixtures with urea solutions. It is a further object to provide a process for the separation of normal parafiins from mineral oil fractions. Other objects will appear hereinafter.

As hereinbefore described, the complex emulsion obtained, takes the form of a thick, thixotropic mass, the thixotropy of the emulsion being caused by the presence in great abundance of the urea/parafiin complex crystals and also by the presence of crystals of urea in excess of saturation at the operating temperature. These complex and urea crystals have a marked tendency to form, by becoming entangled, sufficiently solid structures to offer opposition to the decantation of the droplets of unreacted hydrocarbons (that is, that rafiinate) present in the emulsion. It has now been found that under certain conditions of stirring, as hereinafter described, these tangled crystalline structures tend to disintegrate, thereby facilitating the separation of the liquid phases by decantation.

According to the present invention, there is provided a process for the extractive crystallization of a hydrocarbon mixture comprising hydorcarbons of different chemical type as hereinbefore described, which comprises treating said hydrocarbon mixture with a solution of urea whereby there is formed an emulsion comprising a urea adduction raffinate phase and a phase comprising urea solution, said emulsion containing, in suspension, a solid urea adduct in the presence or absence of solid urea, and prior to and/or during separation of the liquid phases, stirring the mixture by causing a stream of bubbles of an inert gas to pass therethrough, whereby the solid materials pass into the lower, urea solution phase, the separation of the upper rafiinate phase being effected by decantation, thereafter recovering the extract from the remaining liquid phase.

Preferably the process is applied to the treatment of hydrocarbon mixtures comprising normal paraffins in admixture with other hydrocarbons and wherein the normal paraffins are recovered in the extract. The process of the invention has been found to be particularly suitable for the treatment of mineral oil fractions, for example, petroleum distillation fractions for the recovery of normal parafiins.

In the decantation stage, wherein the raffinate is separated from the urea solution phase, it has been found that the rate of bubbling of the gas through the crystal containing emulsion may be adjusted so as to separate rapidly almost the whole of the rafiinate retained by the crystals.

Preferably in order to carry out this bubbling of gas, a gas distributor is provided at the bottom of the vessel in which decantation is carried out, this distributor suitably being in the form of a system of metal pipes or flexible plastic or synthetic rubber tubes, the pipes or tubes being perforated for the passage of the inert gas. By way of illustration, when using metal pipes, for example iron pipes, the perforations may consist of holes 0.5 mm. in diameter and spaced -15 centimetres apart. When employing synthetic rubber or plastic tubes, the perforations may be provided by puncturing the walls of the tubing by means of a needle or similar instrument, the holes being preferably 4-5 mms. part. The pipes or tubing should be laid within the vessel in such manner that an even distribution of bubbles is provided over the area of the bottom thereof.

According to the invention, the gas bubbling output should be suflicient to impart to the mass of the emulsion a jerky movement to break down the conglomeration of crystals and prevent them from reforming. However, the

rate of bubbling of the gas should not be too intensive since, if the motion of the mass of the emulsion becomes too great, there is a tendency for part of the raffinate to reform an emulsion, clearly contrary to the purpose in view.

While any gas which is inert to the materials employed in the process under the conditions of the process may be employed to break down the crystal structures for convenience air is usually employed. It is apparent that a loss of solvent may take place when the inert gas is passed through the emulsion. This may be prevented by providing an entirely closed emulsion breaking and phase separating vessel. Under these conditions, by means of a fan or compressor, gases from the atmosphere of the vessel are taken from a point above the surface of the emulsion and delivered to the gas distributor at the base of said vessel. In this way the inert gas very quickly becomes saturated with vapour and, as it is constantly being circulated through the mass of the emulsion, the losses of solvent may be. eliminated.

The separation of raffinate contained in the emulsion by the process of the present invention is not dependent upon the use of a particular urea solvent in the formation of the complex. If the urea solvent is partially miscible with the hydrocarbons, a mixture of raft'inate and solvent is decanted, and thereafter separated by any suitable means for example, distillation.

By the process of the invention, it is usually possible to separate the bulk of the raflinate from the emulsion within a short period of time, usually ranging from a few minutes to thirty minutes. The time required depends on the consistency of the emulsion. It is, however, virtually impossible to separate, without an additional stage which will be described hereinafter, the whole of the raflinate present in the emulsion, even by extending the period of passing inert gas; indeed, microscopic droplets of raffinate will almost invariably remain fixed to the complex crystals suspended to the urea solution. These droplets are too small to be carried upwards by the gas passing through the mass of the urea solution.

Preferably the extract hydrocarbons, after separation of the rafiinate, are recovered by heating the urea solution with the complex held in suspension in order to destroy the complex, thereby releasing normal and slightly branched parafiins and regenerating urea. In this operation the droplets of raflinate that had remainder fixed to the crystals of the complex, mix with the paraffins obtained by the destruction of the complex. The extract, separated by decanting at the surface of the solution of regenerated urea, therefore contains some highly branched-chained paraffin hydrocarbons, naphthenes and/ or aromatic hydrocarbons, derived from these droplets and constituting an impurity in respect of the normal hydrocarbons. When the urea solvent is suitably chosen, the extract obtained is usually a mixture of about normal paraffin and 20% other hydrocarbons.

This degree of purity, which is, in general, very much greater than that obtainable by the industrial separation processes at present in use in the petroleum industry, provides a suitable feedstock for the manufacture of a large number of chemical derivatives.

According to a further feature of the present invention, normal parafiins with a still higher degree of purity are obtained. Thus according to this further feature, after separating, by gas bubbling, the greater part of the raffinate present in the emulsion, a quantity of a Washing solvent, consisting generally of a mixture of hydrocarbons is added to the remaining urea solution (said solution bearing the complex crystals in suspension). Thereafter, an emulsion of this mixture is formed by any suitable method, such as mechanical stirring.

The stage thus reached is analogous to that which preceded separation of the raflinate from the emulsion by bubbling, the solvent incorporated in the emulsion in the phase, consisting of urea solution and complex crystals, being separable under the same conditions as was the raffinate.

Thus the solvent treated emulsion containing, in suspension, the solid urea adduct in the presence or abscence of solid urea, is stirred by causing a stream of bubbles of an inert gas to pass therethrough, whereby the solid materials in suspension pass into the lower (urea solution) phase, the upper layer, comprising solvent and traces of rafiinate, being simultaneously or thereafter removed by decantation.

In this manner it is possible to effect a washing treatment upon the crystals of the complex in suspension in the urea solution. This washing removes the major part of the microscopic droplets of the rafi'inate which had not been separated by the first operation of decantation.

A variant of this method of washing consists of injecting the washing solvent straight into the feed of inert gas to the gas distributor.

Washing solvent can be formed of any suitable mixture of hydrocarbons, but, preferably, a petroleum fractlon is employed. However, as this washing is aimed at increasing the purity of the normal paraflins resulting from the destruction of the complex, it is usually desirable to select a solvent having a. distillation range that is distinct from that of the extract of normal paraflins to be obtained since, after washing the complex by the petroleum fraction, and after separating the fraction by bubbling through gas, microscopic droplets of this solvent fraction remain fixed to the crystals of the complex.

During the destruction by heat of the complex in suspension in the urea solutionwhereby the extract is freed from urea-the droplets of solvent pass into the extract phase and constitute an impurity in the normal parafiins. When the washing agent used is a petroleum fraction of different volatility, preferably a fraction that is more volatile than the normal paraffins undergoing treatment, the final separation 'of the small amount of washing agent retained by the extract is an easy matter by fresh distillation.

It has been stated that, in general, the process forming the subject of the invention yields, on an average, an extract consisting of a mixture of 80 parts by weight of normal parafiins and 20 parts by weight of raflinate hydrocarbons. By use of the washing stage hereinbefore described, extracts of even higher normal paraffin content is obtained. Thus by way of illustration, with a quantity of solvent equal to three times the amount of normal paraflins to be obtained, i. e. by using 240 parts of solvent to 80 parts of extract parafiins, 20 parts of impurities of normal paraifins are diluted in the proportion 240/20, that is 12/1, so that the 80 parts of normal parafiins to be obtained do not contain more than 20/ 12, that is 1.66 parts by weight, i. e. 2.1% of impurities, representing a very high degree of technical degree purity in this art. These theoretical figures clearly illustrate the potential value of washing by a solvent as herein described.

The quantity of petroleum solvent required for the washing stage is relatively small and in a petroleum refinery the used washing solvent, together with entrained impurities, may be incorporated in fuels or other commercial products manufactured in the refinery. Alternatively the impurities may be separated from this washing solvent distillation.

There is thus achieved, according to the present invention, an extractive crystallization process which may be operated in continuous manner and which involves the following steps:

(1) Reaction of the mixture of hydrocarbons with a urea solution.

(2) Bubbling gas through the product with decantation to remove the rafiinate.

(3) Optionally, adding to the remaining phase a washing solvent and bubbling gas through the mixture with decantation to remove the bulk of the washing solvent.

(4) Heating the urea solution, containing complex crystals in suspension, to regenerate urea and release the normal paraflins with separation of the extract by simple decantation.

The operation of this process does not necessitate the use of expensive equipment, such as rotary filters, centrifuges and provides a means of obtaining, in the one hand, a rafiinate very largely free from normal paraifins and, on the other hand, an extract consisting predominately of normal paraffins.

Preferably the process according to the invention is applied to mixtures of hydrocarbons or petroleum fractions boiling within the range 80-350 C.

Preferably there is employed as solvent for urea in the formation of the urea solution, the solvents particularly described in United States patent application Ser. No. 278,627.

Preferably also the urea employed contains 0.5 to 5% by weight of biuret, as described in United States patent application Ser. No. 286,829.

It has been found that best results are obtained by using a solvent consisting of a mixture of 75 parts by weight of 80% methanol and 25 parts by weight of ethylene glycol, the urea dissolved in this solvent containing 1% by weight biuret.

The invention is illustrated but in no way limited by the following examples.

In these examples the percentages and parts are given by weight.

Example 1 A solution of urea in 90% aqueous methanol wasprepared, which was saturated at 20 C. 12 parts of urea were added to 88 parts of this saturated solution at 20 C. to obtain a solution ofurea which, at 20 C., thus contained 12% more urea than is required for saturation. This solution was heated to dissolve all the surplus urea and then allowed to cool, while stirring vigorously.

With the temperature maintained at 20 C., 300 parts of this saturated urea solution were mixed with parts of a straight run -240 C. fraction of Middle East petroleum. A crystalline complex was formed progressively between the urea and the normal paraflins of the petroleum fraction.

The progress of the reaction was followed by taking a sample of the emulsion formed, centrifuging it to separate the hydrocarbons which had not reacted, and determining the density. The density of the raflinate reached its maximum value after stirring for 20 minutes.

Stirring was then stopped and part of the raifin'ate decanted from the surface. To separate the portion of the raffinate that had remained in emulsion in the urea solution containing complex, the mass was subjected for about 2030 minutes to bubbling by means of air bubbles, the droplets of raifinate which had been held back in the slurry of complex and urea solution being thereby carried into an upper layer upon said solution. The rafiinate was then separated by decantation.

The remaining slurry of complex crystals and urea solution was heated at 60 C. to destroy the complex, thereby freeing the paraffins constituting the extract and regenerating the urea, which remained in the hot solution. The extract, which formed an upper layer, was decanted.

In this operation the following balance was obtained:

Parts Density at 15 C.

Initial charge 100 0.7905 Rafiinate 73 0. 7946 Extract .c 27 0. 7795 Parts Density at 15 C.

It was found that by the method of Examples 1 and 2, the separation of raflinate, by bubbling air, was very clear cut. Moreover, in Example 2, the presence of biuret in the urea greatly assisted the reaction, the resulting raffinate having a higher density (and thus lower normal parafiin content) and the extract having a lower density than that of Example 1, and thus a higher normal paraflin content.

Example 3 A solution as prepared of urea, together with 1% biuret, in a ternary solvent consisting of a mixture of methanol, water and ethylene glycol, the solution having the following'constitution:

Percent Urea containing 1% biureti. 40.5 96% methanol (4% water); 34.3 Water' 10.0 Ethylene glycol 15.2

This solution of urea contained 12% urea in excess over and above saturation at 20 C.

100 parts of a straight run 155240 C. distillation fraction of MiddleEast petroleum was stirred vigorously with 300 parts of the urea solution which had previously been heated to 40 C. to dissolve all the urea (in excess over saturation at 20 C.) then cooled rapidly stirring all the time. The reaction continued with vigorous stirring, the temperature being adjusted to 20 C. The progress of' the reaction was followed by studying the increase in the density of the fractions of the raffinate obtainedby successively centrifuging out samples from the emulsion.

The maximum density was reached after 30 minutes stirring, which indicated that all the normal paraffins capable of forming a complex with urea at 20C. had been eliminated from the liquid phase.

The rafiinate was then separated by decanting, while bubbling air through the emulsion for 15 minutes, thereby breaking down the emulsion and permitting separation of the majority of the droplets of the rafiinate trapped in the complex crystals.

The urea solution/ complex slurry was heated to 60 C.

Parts Density at 15 C Initial charge 100 0. 8905 Refined product... 84 0.796 Extract; l6 0. 760

The extract thus obtained contained 79% paraflins.

normal Example 4 The operation described in Example 3 was repeated to the stage at which the raffinate was separatedby' decanting, under the action'of air bubbling.

After separating the rafiinate, the complex/urea solution slurry was mixed for 5 minutes with 30 parts of a 100-120 C. petroleum fraction under the action of mechanical stirring which emulsified the washing solvent in the phase formed by the solution of urea and complex. The washing solvent was then rapidly separated by decantation while bubbling a moderate amount of air into the mass of the emulsion. The decanted washing solvent carried along with it the greater part of the droplets of raflinate that'had remained trapped in the crystals of the complex. The separated washingsolvent was'distilled to recover raffinate contained therein, this raffinate frac-' tion being added to the raflinate fraction obtained in'the first decantation stage.

The complex/urea solution slurry was heated at 60 C. to destroy the complex and free the urea.- The extract was separated by decantation from the solution of regenerated urea and contained-a-small amount of washingsolvent that had remained attached to the crystals of the complex. This washingsolvent was separatedby distillation.

The following balance was obtained:

paraflins.

On comparing the results obtained in Examples 1, 2 and 3, the irnproved selectivity obtained by using a solution of urea, containing biuret, in the ternary solvent methanol-water-ethylene glycol will be apparent.

A comparison of Examples 3 and 4 shows the great improvement in selectivity resulting from the introduction of the washing stage. Example 4 illustrates the manufacture of normal parailins having a very high degree of purity.

The invention is further illustrated but in no way limited with reference to the accompanying drawings in which Fig. .l is a diagrammatic representation of an industrial installation for the continuous operation of the process of the invention, and in which Fig. 2 is a semidiagrammatic view in horizontal section and with parts in section of an emulsion separator such as is used in the installation of Fig. 1.

A petroleum fraction, constituting the feedstock, is delivered by pump 3 to line 21 and blended with a recycle material. This recycle material consists of an emulsion of urea solution and raifinate containing complex crystals and solid urea in suspension and isdelivered by pump 4 and line 25. The blend is passed by line 24 and further blended with urea solution. The urea solution is supplied from storage tank 1 which is maintained at a temperature of 42 C., that is, slightly above urea saturation temperature, by the provision of a hot air jacket (not shown in the drawing). The provision of an air jacket is desirable to avoid local over-heating which would cause hydrolysis of the urea. Urea solution is delivered by pump 2 to line 23 and after blending with materials from line 24 is passed by line 22 to mixer pump 5. The intimate mixture which takes place in line 22 and in pump 5 produces the emulsion required for the reaction.

The blending in of the recycle stream in the manner described is desirable since by operating in this manner it is possible to prevent the charge of fresh feedstock from directly contacting urea solution at 42 C. (which might lead to'frequent stoppages of the lines). Furthermore the recycle material at 20 C., meeting the urea solution at 42 C. causes a sudden and effective cooling of the latter, which is favorable to the formation of urea crystals ofsmall dimension and therefore also favorable to the rapid [formation of the complex.

The emulsion delivered by pump 5 is further cooled by passagethrough heat exchanger 6 to which cold water or any other suitable cooling fluid is supplied by line 7 andremoved 'by line 7'.

The cooled emulsion is withdrawn at 17 C. by line 29 and is passed to reactor 8, thence by line 30 to reactor 9; Recycle emulsion is withdrawn from line 30 by pump 4 and is returned for blending with fresh feedstock by line-25. During the passage through the reactors-the temperature rises from 17 C. to 20 C.

The reactors 8 and 9 are fitted with mechanical stirrers 31- and 32 respectively. From the top half of the reactor 9, the reacted emulsion passes into the separator 10.

The separator 10 is entirely closed and has a horizontal b'ase 'ab'ove' which is mounted a gas distributor 10a. This distributor takes the form of a number of synthetic rubber pipes, having small perforations in their walls,

- the pipes being evenly set out over the base of the separator. A fan 11 has an intake at the top of the separator 9 10 and continuously recycles gas to the distributor 10a, where the gas is forced out of the perforations, bubbles of gas (10b) thus constantly ascending through the emulsion. The delivery of these gas bubbles 10b is regulated to effect the breakdown of the emulsion and carries to the surface drops of raffinate entrapped in the solid material suspended in the liquid phase.

Advantageously, the separator 10 may comprise a casing 41 as is depicted in Fig. 2. Headers 42 and 45 disposed at opposite ends of the casing are provided each with corresponding number of outlet pipes 43 connected together by synthetic rubber pipes 44, each having small perforations 46 in their upper surface. A feed pipe 40 is connected to one or the other of the headers 42 and 45 and serves to supply recycled gas to the distributor to be forced out of the perforations 46 as above described. The feed pipe 40 is connected to the header 42 as shown in Fig. 2 but it will be understood that the connection may be made to either or both of the headers.

Raffinate leaves the separator 10 by line 33 and can be washed subsequently with water.

Urea solution/complex slurry, carrying with it micro scopic droplets of entrained raffinate, is removed from the bottom of the separator by pump 12. This pump 12 is also supplied with a washing solvent consisting of a petroleum fraction which is more volatile than the petroleum fraction treated in the installation. Pump 12 emulsifies the washing solvent with the slurry, thereby producing intimate contact between the washing solvent and the crystals and freeing the latter from the remaining droplets of ratfinate.

The emulsion then passes into the separator 14 in which it is broken by gas bubbles 14b from distributor 14a which is identical, in construction, to the distributor 10a of separator 10. Gas from the top of the separator 14 is recycled by fan 13.

Washing solvent is separated at the surface and drained off at line 26. It carries away in solution the greater part of the droplets of raffinate derived from the slurry leaving the separator 10.

When the process forming the subject of the invention is employed in a petroleum refinery, the waste washing solvent can, advantageously, be incorporated in liquid fuels. Alternatively, this solvent can be blended with the feedstock to a redistillation unit for the production of, for example, solvents or white spirit. It is also possible to redistill the Washing solvent to recover the pure solvent and recycle it to separator 14, the small quantity of raffinate recovered in redistillation being added to the raffinate recovered by line 26.

The complex/urea solvent slurry, after being washed by the washing solvent, is taken from the bottom of the separator 14 by pump 15, which delivers it to a heater 16 which is heated by steam or hot air to provide a product outlet temperature of 60 C. In the heater the complex is broken down, liberating, on the one hand, the extract consisting of normal parafiin and, on the other hand, the urea which passes into solution and reconstitutes the original urea solution. The two phases are separated in the separator 17 by simple decantation at 60 C. The extract is drawn off at the surface by line 27.

The urea solution at 60 C. still contains, dissolved or in suspension, a small quantity of extract. It is passed to a cooler 18, which lowers the temperature to 42 C., then to a separator 19 kept at 42 C. At that temperature a further quantity of extract separates and is drawn otf at the top of the separator by line 28. The extract can thereafter be washed with water (in an apparatus not shown in the drawing) and distilled to remove traces of the washing solvent contained therein.

The urea solution at 42 C. is collected by a pump 20 which delivers it by line 34 to the urea solution tank 1.

In the interests of simplicity, the drawing does not the separation of normal parafiins from mixtures of normal olefins and normal diolefins; or for the separation of normal olefins from normal diolefins. All the above variants of the process hereinbefore described lie within the scope of the present invention.

We claim:

l. A process for the extractive crystallization of a hydrocarbon mixture containing only in part hydrocarbons capable of forming urea adduct which comprises treating said hydrocarbon mixture with a solution comprising urea whereby there is formed an emulsion consisting of a liquid phase comprising a urea adduction raffinate and a liquid phase comprising urea solution, said emulsion containing a solid phase in suspension, said solid phase comprising a crystalline urea adduct, stirring the mixture by causing a stream of bubbles of an inert gas to pass therethrough, whereby there is formed an upper liquid phase comprising ratfinate and whereby the solid materials pass into the lower liquid phase comprising urea solution, separating the upper phase by decantation and recovering hydrocarbons from the solid urea adduct contained in the remaining liquid phase.

2. A process as specified in claim 1 in which the hydrocarbon mixture is a petroleum distillation fraction having an initial boiling point above C. and a final boiling point below 350 C.

3. A process for the extractive crystallization of a hydrocarbon mixture comprising, only in part, hydrocarbons capable of forming urea adducts, which process comprises treating said hydrocarbon mixture with a solutioncomprising urea whereby there is formed an emulsion consisting of a liquid phase comprising a urea adduction raflinate and a liquid phase comprising urea solution, said emulsion containing a solid phase in suspension, said solid phase comprising a crystalline urea adduct, stirring the mixture by causing a stream of bubbles of an inert gas to pass therethrough, whereby there is formed an upper liquid phase comprising rafhnate and whereby the solid materials pass into the lower liquid phase, separating the upper phase by decantation, heating the remaining liquid phase whereby the solid urea adduct is decomposed with liberation of the extract hydrocarbons and reformation of urea solution and thereafter separating the extract hydrocarbons from the urea solution.

4. A process for the extractive crystallization of a hydrocarbon mixture containing only in part hydrocarbons capable of forming urea adducts which comprises treating said hydrocarbon mixture with a solution comprising urea whereby there is formed an emulsion consisting of a liquid phase comprising a urea adduction raffinate and a liquid phase comprising urea solution, said emulsion containing a solid phase in suspension, said solid phase comprising a crystalline urea adduct, stirring the mixture by causing a stream of bubbles of an inert gas to pass therethrough, whereby there is formed an upper liquid phase comprising raffinate and whereby the solid materials pass into the lower liquid phase comprising urea solution, separating the upper phase from the product by decantation, mixing the remaining product with a washing solvent selected from the group consisting of hydrocarbons and mixtures thereof, stirring the mixture by causing a stream of bubbles of an inert gas to pass therethrough, whereby there is formed an 11- upper liquid phase comprising washing solvent and whereby the solid materials pass into lower liquid phase comprising urea solution, separating the upper phase by decantation, and recovering hydrocarbons from the solid urea adduct contained in the remaining liquid phase.

5. A process for the extractive crystallization of a hydrocarbon mixture containing only in part hydrocarbons capable of forming urea adducts which comprises treating said hydrocarbon mixture with a solution comprising urea whereby there is formed an emulsion consisting of a liquid phase comprising a urea adduction rafiinate and a liquid phase comprising urea solution, said emulsion containing a solid phase in suspension, said solid phase comprising a crystalline urea adduct, stirring the mixture by causing a stream of bubbles of-an inert gas to pass therethrough, whereby there is formed an upper liquid phase comprising rafiinate and whereby the solid materials pass into the lower liquid phase comprising urea solution, separating the upper phase from the product by decantation, mixing the remaining product with a washing solvent selected'from the group consisting of hydrocarbons and mixtures thereof, stirring the mixture by causing a stream of bubbles of an inert gas to pass therethrough, whereby there is formed an upper liquid phase comprising washing solvent and whereby the solid materials pass into the lower liquid phase comprising urea solution, separating the upper phase by decantation, heating the remaining liquid phase whereby the solid urea adduct is decomposed with liberation of the extract hydrocarbons and reconstitution of the urea solution and thereafter separating the extract hydrocarbons from the urea solution.

6. A process as specified in claim 5 in which the washing solvent is a hydrocarbon mixture having a boiling range below the boiling range of the hydrocarbon mixture undergoing treatment.

7. A process as specified in claim 5 in which the petro leurn fraction has an initial boiling point above 80 C. and a final boilingpoint below 350 C.

8. A process as specified in claim 5 in which the inert gas is air.

9. A process for the extractive crystallization of a petroleum distillation fraction having an initial boiling point above 80 C. and a final boiling point below 350 C., which comprises mechanically stirring said fraction with a supersaturated solution of urea, said urea solution containing 05-50% by weight of biuret, basedon the weight of urea, said urea and biuret being dissolved'in a solvent comprising a major proportion of methanol together with a minor proportion of water and a minor proportion of ethylene glycol, by which treatment there is formed an emulsion consisting of a liquid phase comprising a urea adduction rafiinate and a liquid phase comprising urea solution, said emulsion containing, in suspension, a crystalline urea'adduct and solid urea thereafter further stirring the mixture in aclosed vessel by recycling air therethrough, said air'passing. upward through the mixture in the form of fine bubbles, whereby there is formed an upper liquid phase comprising raffinate and whereby the solid materials pass into the lower phase, separating the upper phase from the product by decantation, mechanically stirring the remaining product with a washing solvent selected from the group consisting of hydrocarbons and mixtures thereof, thereafter further stirring the mixture in a closed vessel by recycling air therethrough, said air passing upwards through the mixture in the form of fine bubbles, whereby thereis formed an upper liquid phase comprising washing solvent and whereby solid materials pass into the lower phase, separating the upper layer by decantation, heating the rcmaining liquid phase whereby the solid urea adduct is decom posed with liberation of the extract'hydrocarbons and reconstitution of urea solution and thereafter separating the extract hydrocarbons from the urea solution'by decantation.

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1. A PROCESS FOR THE EXTRACTIVE CRYSTALLIZATION OF A HYDROCARBON MIXTURE CONTAINING ONLY IN PART HYDROCARBONS CAPABLE OF FORMING UREA ADDUCT WHICH COMPRISES TREATING SAID HYDROCARBON MIXTURE WITH A SOLUTION COMPRISING UREA WHEREBY THERE IS FORMED AN EMULSION CONSISTING OF A LIQUID PHASE COMPRISING A UREA ADDUCTION RAFFINATE AND A LIQUID PHASE COMPRISING UREA SOLUTION, SAID EMULSION CONTAINING A SOLID PHASE IN SUSPENSION, SAID SOLID PHASE COMPRISING A CRYSTALLINE UREA ADDUCT, STIRRING THE MIXTURE BY CAUSING A STREAM OF BUBBLES OF AN INERT GAS TO PASS THERETHROUGH, WHEREBY THERE IS FORMED AN UPPER LIQUID PHASE COMPRISING RAFFINATE AND WHEREBY THE SOLID MATERIALS PASS INTO THE LOWER LIQUID PHASE COMPRISING UREA SOLUTION, SEPARATING HYDROCARBONS FROM THE SOLID CENTATION AND RECOVERING HYDROCARBONS FROM THE SOLID UREA ADDUCT CONTAINED IN THE REMAINING LIQUID PHASE. 